1. Field of the Invention
The invention relates to tactile devices for producing a signal preceivable as an audio signal, which may be used as a hearing aid.
2. Description of the Prior Art
Tactile hearing aids are known, for example in U.S. Pat. No. 4,139,742, wherein communications, principally acoustical information such as speech, are converted into electrical signals which are then transmitted by mechanical stimulation to the surface of the skin, i.e., to the sense of touch. Messages can still be conveyed with this hearing aid even when they could not be perceived by normal bearing because of a loud and unsurveyable environment because of a hearing deficiency or when an acoustical perception is impossible because of deafness. Like standard hearing aids, these systems should also be an unobtrusive as possible and should be capable of being used without significant negative effect on the activities of daily life. What is required for this purpose is an arrangement which is light and small and which operates with a low power consumption so that it can be operated with portable current sources such as batteries. Only in this fashion is a device independent of the mains and of the type which can be unobtrusively carried. The power consumption should be able to be maintained at least for the duration of ten hours by means of mobile current sources such as batteries without an interruption being required.
It has proven beneficial, particularly in hearing aids for extremely pronounced reductions in the hearing faculty, to make use of tactile transmission. In comparison to electrocutaneous system, improved chronological resolution of the sense of touch and better time invariancy of the threshold of sensation are achieved among other things. Heretofore, however, suitable electro-mechanical transducers have been lacking. Particularly in multi-channel devices and vocoder systems, for instance those known from French Pat. No. 12 31 085, conventional electro-mechanical transducers cannot be used because they are too heavy and too large. The demands for low volume and low weight cannot be met with the standard electromagnets due to the physical principle employed.
Even piezoceramic transducers employed in more recent systems known, for instance, from the publication by T. Ifukube, "A Cued Tactual Vocoder" in JFGP-JMJA Working Conference on Uses of Computers in Aiding the Disabled, Haifa, 1981, containing flexural resonators working according to the bimorph principle have not gained acceptance. The piezoceramic provided for the manufacture of these resonators is extremely sensitive in mechanical terms. It must therefore be adequately protected, whereby the necessary volume must be increased beyond an acceptable degree.
Numerous investigations have shown that the hand is best suited for the transmission of audio signals via multi-channel systems upon employment of vibrations. The breakable ceramic elements, however, are exposed to particularly severe mechanical demands when worn on the hand.